1. Field of the Invention
The present invention relates to a structure of a rectilinear motion rolling guide unit such as ball bushing, ball spline linear motion rolling guide unit or the like comprising a long cylindrical shaft member, a hollow cylindrical outer cylinder member having a hollow hole to slidably insert the cylindrical shaft member therein, and a number of balls which are inserted between both of those members and are endlessly circulated.
2. Description of the Related Background Art
As such a kind of rectilinear motion rolling guide unit, there has been known a ball spline linear motion rolling guide unit disclosed in Japanese Patent Application No. 231514-1987. The above guide unit comprises: a ball spline shaft on which a plurality of track grooves are formed in an axial direction at predetermined positions on the outer peripheral surface; an outer cylinder member which has a hollow cylindrical outer cylinder having a hollow hole into which the ball spline shaft is slidably inserted and in which track grooves which face the track grooves of the ball spline shaft are formed on the hollow inner peripheral surface and ball return holes communicating with those track grooves are formed in the outer cylinder member; and a number of balls which are inserted between the track grooves of the spline shaft and outer cylinder member. According to such a construction, side plates attached respectively to both end portions of the outer cylinder member, that is, a spacer ring 3' as an inside plate as shown in FIGS. 6 and 7 and an outside plate 4' are combined at surfaces respectively shown in the diagrams, thereby forming a ball direction turning passageway. An outer peripheral wall surface 4'a in the U-turn portion of the direction turning passageway is formed like a groove on the outside plate 4' (FIG. 7). On the other hand, the adjacent portions of the openings of the track side portion 4'a of a direction turning passageway 7' and of a return passageway side portion 4'b communicating with the track side portion 4'a are coupled with the confronting surface of the spacer ring 3' (FIG. 6) as the inside plate to be combined with the outside plate 4'. Thus, an inner peripheral wall 3'a of the turning passageway U-turn portion in the ball direction in the side plate is formed by a coupling surface 4'c as shown in FIG. 6.
FIG. 5b is a cross sectional view in the radial direction of the outer cylinder of the linear motion rolling guide unit in the prior art mentioned above. FIG. 5a is a diagram in the case where the direction turning passageway portion in FIG. 5b is seen from the top position. As clearly illustrated in FIG. 5a, in the conventional guide unit, a height different portion occurs in the outer peripheral wall surface portion 4'a of the direction turning passageway in the confronting surface boundary portion between the outside plate 4' and the spacer ring 3'.
In general, those side plates are formed by injection molding a synthetic resin material. In this case, since the inside die of the direction turning passageway portion of the spacer ring 3' is pulled out in the direction of the outside plate 4', it is impossible to form a trimming die such that it becomes narrow in the trimming direction in accordance with the outer peripheral wall surface 4'a of the direction turning passageway of the outside plate 4'. Therefore, it cannot help forming the outer peripheral wall surface which is almost parallel with the trimming direction.
Thus, there is a drawback such that a height different portion occurs in a part of the outer peripheral wall surface 4'a of the direction turning passageway as shown in FIG. 5a and the balls which are circulated in this portion do not smoothly move.